title: PAIN with and without PAR: variants for third-spin assisted heteronuclear polarization transfer.
abstract: In this article, we describe third-spin assisted heteronuclear recoupling experiments, which play an increasingly important role in measuring long-range heteronuclear couplings, in particular (15)N-(13)C, in proteins. In the proton-assisted insensitive nuclei cross polarization (PAIN-CP) experiment (de Paëpe et al. in J Chem Phys 134:095101, 2011), heteronuclear polarization transfer is always accompanied by homonuclear transfer of the proton-assisted recoupling (PAR) type. We present a phase-alternating experiment that promotes heteronuclear (e.g. (15)N → (13)C) polarization transfer while simultaneously minimizing homonuclear (e.g.(13)C → (13)C) transfer (PAIN without PAR). This minimization of homonuclear polarization transfer is based on the principle of the resonant second-order transfer (RESORT) recoupling scheme where the passive proton spins are irradiated by a phase-alternating sequence and the modulation frequency is matched to an integer multiple of the spinning frequency. The similarities and differences between the PAIN-CP and this het-RESORT experiment are discussed here.
authors.affiliation: Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland.
authors.forename: Vipin
authors.initials: V
authors.lastname: Agarwal
authors.forename: Mariana
authors.initials: M
authors.lastname: Sardo
authors.forename: Ingo
authors.initials: I
authors.lastname: Scholz
authors.forename: Anja
authors.initials: A
authors.lastname: Böckmann
authors.forename: Matthias
authors.initials: M
authors.lastname: Ernst
authors.forename: Beat H
authors.initials: BH
authors.lastname: Meier
mesh_terms: D003198:Computer Simulation; D003460:Crystallization; D019906:Nuclear Magnetic Resonance, Biomolecular; D011522:Protons; D013113:Spin Labels; D025801:Ubiquitin / Q000737:chemistry
chemical_list: D011522:Protons; D013113:Spin Labels; D025801:Ubiquitin